SUMMARY:
The effects of SMF on nerve conduction are unclear and the underlying mechanisms not well understood. This study focused on the effects of a moderate (iSMF) on membrane excitation and refractory processes on frog sciatic nerve fibres.

Nerve conduction velocity (NCV) was measured and compared within three groups, a control and a 0.21Tesla and 0.7Tesla iSMF.

Effect of control (black) and two different iSMF’s on Nerve Conduction Velocity

The researchers speculate that the action of moderate-intensity iSMF may act in a similar way to that of Na+ channel-blocking anaesthetics. With regard to nerve conduction, iSMF did not affect large diameter, myelinated, fast conducting nerve fibres, but only small diameter, unmyelinated, slow conducting C-fibres. This may be due to the fact that C-fibres possess a relatively greater density of voltage gated Na+ channels.

These findings are consistent with that of McLean et al. in that an iSMF has a negligible effect on fast as compared to slow conducting nerves. Fast conducting nerves such as Aβ and Aδ fibres are responsible for proprioception and the withdrawal reflex so the body’s natural warning and protective mechanisms still function as normal. However nociceptors, the small C-fibres responsible for the dull ache are likely to be less sensitive to a pain stimulus when in the presence of an optimised iSMF. The dampening or calming down of sensitized C-fibres can increase the pain threshold and improve the quality of life of pain sufferers.